Add admin interface to the checkouts app.

mayan/apps/checkouts/admin.py

@@ -0,0 +1,14 @@
+from __future__ import unicode_literals
+
+from django.contrib import admin
+
+from .models import DocumentCheckout
+
+
+@admin.register(DocumentCheckout)
+class DocumentCheckoutAdmin(admin.ModelAdmin):
+    list_display = (
+        'document', 'checkout_datetime', 'expiration_datetime', 'user',
+        'block_new_version'
+    )
+    list_display_links = None